It is well-known, for example, that the fluidity of gas oils used for motor vehicles, for naval and aircraft engines or for heating, decreases when the temperature lowers, causing quite serious inconveniences.
The above phenomenon is mainly due to the precipitation of n-paraffins contained in the gas oil.
It is also well-known that such inconveniences can be overcome by the addition to the above hydrocarbons of suitable products, normally polymeric substances.
The additives which are normally used for this purpose are ethylene/vinylacetate copolymers of a particular molecular weight and composition, or ethylene/propylene/unconjugated diene copolymers and terpolymers, prepared by using homogeneous catalysts (based on vanadium and aluminium organometallic compounds) as described in the Italian patents N. 811,873 and 866,519.
The U.S. Pat. Nos. 3,374,073 and 3,756,954 propose as additives the ethylene/propylene/conjugated or unconjugated diene terpolymers, prepared by using homogeneous catalysts, which suffered degradation to certain values of molecular weight, through thermal oxidation.
The most common additives for gas oil or Middle Distillate allow the use of these hydrocarbons also at low temperatures in that, by interfering on the crystallization kinetics, they determine the form and dimensions of the crystals and also restrain the crystallization and agglomeration of crystals, thus improving the liquid flow. Said additives, therefore, do not modify the cloud point of the hydrocarbon compounds, i.e. the temperature of the first appearance of the paraffin crystals in the liquid.